Directional stabilizer



Feb. 26, 1929. H 1,703,280

N. MINORSKY DIRECTIONAL STABILIZER Filed Sept. 21, 1922 4 Sheets-Sheet 1 Z8 g/se nmhlmh gig g2? Fl g I IN VEN TOR.

N/COLA/ MINORS/C Y BY wu A TTORNEY Feb. 26, 1929. 1,703,280

.N. MINORSKY DIRECTIONAL STABILIZER Filed Sept. 21. 1922 4 Sheets-Sheet 3 IN V EN TOR.

NICOLA MINOESKY E1 By A TTORNE Y Feb. 26, 1929. 1,703,280

N. MINORSKY DIRECTIONAL STABILI ZER Filed Sept. 21. 1922 4 Sheets-Sheet '4 IN V EN TOR.

N/COZA M/NOESK Y BY ZZa/M/ ATTORNEY Patented Feb. 26, 1929.

PATENT OFFICE.

NICOLAI MINORSKY, OF BELMAR, NEWzJERSEY.

DIRECTIONAL STABILIZER.

Application filed September 21, 1922. Serial No. 589,627.

This invention relates to the control of stabilization of ships, airships, airplanes and the like,in response to the combined effect of the angular deviation of the body to be stabilized from its predetermined direction, and also ofone or more time derivatives of this deviation. I

The advantages of controlling the stabilization in response to such a combination of dynamical elements have been set forth at length in my }Patent 1,436,280, of November 21, 1922, entitled Automatic steering device. In that application I describe specifically a helm controlling device for a ship, so arranged that the movements of the rudder are affected in response to the yawing of the ship off her course, and to a plurality of higher time derivatives of the yawing, especially the velocity and the acceleration of the yawing. It is possible to demonstrate mathematically that it is essential to control the rudder or other stabilizing device in response to such a function in order that the directional stability along the course be performed in a substantially:perfect dead beat manner; and if on the contray this control be made responsive solely to the extent of. deviation from the predetermined directlon, oscillations of the controlled body about the desired line of stabilization cannot be prevented. The principles involved forv proper dead beat stabilization are of course applicable to other cases, where it is desired to maintain the relative position of a body fixed with respect to a reference line or to another body.

Such a case, for example, arises in connection with airplanes where stabilization may be desirable about more than one axis.

It is one of the objects of my invention to provide a comparatively inexpensive and simple device for effecting substantially the .same results as in my prior application. "Furthermore the present application describes a device having comparatively small weight, so that it is especially applicable for the stabilization of airplanes.

' Another object of myinvention is to provide a controlling device for stabilizing which is devoid of either gyroscopes or follow tially no contacts to; be made and broken. The avoidance of contact making devicesgis at any time.

up devices, and instead makes use of Sta-.- tionary electrical apparatus with substanof especial importance where the control is mounted on bodies subject to violent vibrations, such as airplanes, since such contacts as is apparent may be seriously and objectionably affected by these vibrations.

Another advantage secured by my invention resides in the degree of facility with which the control may be adapted to any particular body to be steered or stabilized, and to vary the performance of the control to suit weather conditions or the requirements of navigation either in the air or on the Water To produce these variations or adjustments with my controlling deviceis an extremely simple matter, as it may be effected by adjustment or tuning of the electrical constants of controlling circuits, as for example by a variation in inductance or resistance, or

both. I

To provide this simplicity of control, I

make use of a device that is moved in and influenced by the earths magnetic field so as to generate an E. M. F., such as a constantly revolving armature of the direct current type.

It is thus another object of my invention to utilize as a control element a device for generating an E. M. F. by rotation in the terrestrial magnetic field.

It is still another object of my invention to provide an extremely simple manually operated steering device by which it is possible to set the course of the body so that the auto- 'matic control will bring the body back to that set course in response to functions of its de-, viation.

My invention possesses many other advantages, and has other objects which may be made more easily apparent from a consideration ofvarious embodiments of the invention. For this purpose I have shown several forms of my invention in the drawings accompanying and forming part of the present specification. I shall now proceed to describe in detail these forms, which illustrate :the general principles of my invention, but

it is to be understood that this detailed description is not to be taken in a limiting sense,

sinceI intend the scope of my invention to be defined by the appended claims.

' Referring to the drawings:

Figure l is a wiring diagram of one form of control embodying my invention;

Fig. 2 is a diagrammatic longitudinal sec- Fig. 4c is a wiring diagram of amodified form of my invention;

Fig. 5 is av diagrammatic view of a still further modification;

Fig. 6 is a wiring diagram-showing the use of a modified form of thermionic relays or amplifiers used in the circuits of Fig. 1; and

Fig. 7 is a vector diagram illustrating the behavior of the instrument shown in Figs. 2 and 3 under certain conditions.

In Fig. 1, I-illustrate an instrument 11 having a rotating element 12, which is arranged to be influenced by the terrestrial magnetism. The direction of the horizontal component of this field is represented by the large dotted arrow 13 the point of which is labelled North, and is shown in-this instance to be substantially perpendicular to the axis of rotation of the element 12. This element is constructed like an ordinary bipolar direct current armature, as indicated more clearly in Fig. 2, and is provided with commutator 14 upon which bear the brushes 15, 16. Any appropriate source of motion such as a motor 17 may bearran'ged which the armature sweeps.

to rotate the armature 12, as by direct connection to the shaft 18 of the-armature. The

I electromotive force which is induced across the brushes 15, 16, due to the motion of armature 11 in the terrestrial field, depends, among other things, upon the relative position of the brush axis and of the axis of the'field through In the present instance it is' assumed that when the brush axis is parallel with the direction of the earths field as illustrated in Fig. 1, the potential difference across the brushes is a minimum, or zero. As is well understood deviation of the brush axis from this position causes the potential difference to be increased substantially as a sine function of the angle of deviation. I urthermore it may be assumed that a deviation in a clockwise direction, as shown by the arrow 19, results in making the upper brush 15 positive with respect to the lower brush 16. Deviation inthe opposite direction causes this polarity to be reversed.

By fixing the brush axis so that it. has a definite direction with respect to that of a chosen axis of the body to be. stabilized, deviations of this latter axis from a definite direction causes corresponding variations of the. induced electromotive force for influencing the stabilizing element, which may be a rudder 170 arranged to be effective by its movement to bring the body back to its predetermined position. In .the present instance the electric motor 20 of the directcurrent type is ar in response to functions of the deviation of the brushes from the minimum or zero E. M. F. position, so as to impress upon the armature of motor 20, electromotive forces which vary correspondingly to the variations in the controlling functions. The generator 21 may be driven by any appropriate source; if the installation is on an airplane, the generator may be driven by the shaft 23 carrying the screw 24 whichis adapted to be rotated by the relative movement of the airplane with respect to the atmosphere. The shaft 25 of the motor 20 is connected in any appropriate way to the .rudder moving mechanism.

The generator 21 not only serves to transmitproperly the functions ofthe variations in the E. M. F. across the brushes 15 and 16, to the motor 20, but also serves to magnify or amplifythese eifects. The functions of the E. M. F. which are most useful for stabilizing the body, are those due to the deviation of the brushes from zero position and derivatives of this E. M. F. with respect to time. Since the the extent of deviation of the body, in con' junction with't-he velocity of deviation, and if necessary, with still higher time derivatives of the deviation, such as the acceleration and the velocity of acceleration.

In order to magnify or amplify the effects of the deviation and its dynamical elements before they are caused to affect the generator 21, appropriate relays may be provided. These relays may be of the electromagnetic type, but in order to cause as prompt response of the entire control to the conditions of the deviation as possible, I prefer to use thermionic relays, such as 26, 27, and 28. These have the further advantage that no circuits need be made or broken by them, and they act in a perfectly continuous manner. Before discussing in greater detail the circuits of Fig. 1 whereby these relays and the generator 21 properly affect the motor 20, it is advisable to describe in greater detail one form of the instrumentality 11 which forms the seat of the controlling forces for the entire device. Thils instrument is shown in detail in Figs. 2 ant 3.

In the present instance the nstrument It is shown as arranged to be affected by the, horizontal component only (3fthe earth's magnctic. field, and in this way it may be made to stabilize a body about a definitely directed horizontal axis or course. In other words, such anlnstrument 1s of use for steering a course with respect to the earths surface. By

deviation of the brushes from the zero potenlit) arranging the instrument so that the armature 12 has its axis rigidly fixed with respect to the body to be stabilized, it is possible to derive controlling functions and obtain controllingactions responsive to deviations in the position of the body not only in azimuth but also in other planes of reference. The axis of armature -12 may for example be so supported on the body that when that body is properly positioned, this axis is parallel to the axis of terrestrial magnetism which is generally known for any given locality; Deviations from this position of the body give rise to the generation of electroi notive forces within the armature which may be utilized to stabilize the body against'rolling and pitching, in addition toeontrol for azimuthal or anti-yawing stabilization. Controlling effects may thus be derived" for all three degrees of freedom of a body, which effects can be made responsive not only to the actual deviation in each degree of freedom but also higher time derivatives of the deviations. This response to deviation in any of the degrees of freedom is of especial importance in connection with the stabilization of airplanes and the like, the position of which is affected by any external disturbance such as Winds, usually in any or all of the three degrees of angular freedom about the center of gravity of the body.

The shaft 18 of armature 12 in the embodiment of Figs. 2 and 3 is shown. so chosen that it occupies a substantially constant vertical direction, irrespective of the movement of the body itself, and in this way the horizontal component only of the terrestrial magnetism is caused to affect the instrument 11. In this way variations of the body from a desired horizontal course on the earths surface cause variations in the relative position of the brush axis and the magnetic meridian, as explained hereinbefore. The armature 12 is constructed substantially like an ordinary direct current armature, except that the number of turns of the Winding in series between brushes 15, 16.is very large, so that a substantial-E. M. F. may be induced across them in spite of the weakness of the terrestrial magnetism in which the armature rotates. For this reason also the armature 12 should be driven at a fairly rapid rate. The cross section of the wire may be very small indeed, since thearmature has to carry minute currents only. Preferably, also, a nonmagnetic core is used for the armature, in order to prevent any distortion of the terrestrial field. The entire mechanism is enclosed in a frame 29 suspended in a C ardan suspension so as to keep the axis of armature 12 vertical. This suspension comprises the usual external gimbals 30, in which is suspended onball bearings 31, the inner gimbals 32. This latter in turn supports on ball bearings 33 the frame29. The axis of bearings 33 is substantially perpendicular to that of bearings 31. By providing a slight amount of pendulousness to the suspended frame 29 and its contents, the axis of armature 12 has a tendency to remain truly vertical, and is not disturbed materially by the angular motions of pitching and rolling of the ship or other body that is being stabilized, since such motions are but little assisted by the natural period of oscillation of the device. Other temporary ballistic disturbances which cancel out over a more extended period are likewise ineffective. Located conveniently near the bottom ofthe frame 29 is the driving motor 17. The shaft 18 is properly supported at an intermediate point by the ball races 34, which act against ashoulder on the shaft and thus serve also as step bearings. These races are supported on the bracket 37 fixed to the interior of frame 29. At the upper end the shaft is guided by the ball bearing 35, held in the cover 36 of the frame 29. The brush-es 15, 16 are supported on the interior of a collar 38 rotatably mounted in bracket 39- fastened to the interior of frame 29. The collar 38 is carried by a non-magnetic rectangular frame 40 encompassing the armature 12. This frame carries in turn the rectangular coils 41 and 42, the turns of which are preferably uniformly distributed along the width of the frame 40, and so arranged that their axis is perpendicular to that of the brushes 15, 16. The entire frame 40, with collar 38 and brushes 15, 16 is rotatable and is supported and guided at the bottom on the stationary collar 43, upon which also rest the bearings 34. In order to rotate this frame, it is adapted to be driven by spur gears 44, 45, which are carried by the frame. The connections to brushes 15, 16 are effected by the aid of terminal posts 46 supported on the cover 36, which'posts connect to the slip rings 47 These ringsare supported on the projection 48 of the cover 36, and are in turn connected by auxiliary brushes. to the main brushes 15, 16. The connections to coils 41 and 42 are effected by the aid of three slip rings 49, 50, and 51, held on the exterior of a collar 52 attached in any suitable manner to, the frame 40. The particular utility of coils 41 and 42 will be described hereinafter, in connection with the detailed description of the ciruits of Fig. 1. i v The motor 17, in addition to its function of rotating the armature 12 at a rapid rate, serves to rotate the whole frame 40 and its associated coils 41 and 42 and brushes 15 and '16, when it is desired to set these brushes to a new position with respect to the body to be stabilized. For this purpose there may be provided a worm 53 on the armature shaft 18, which worm is adapted to engage a worm wheel 54 fastened on shaft 55 journaled appropriately in relatively stationary parts of the frame v29, one of which is shown as the bracket 56 and the other as the side of the frame 29, Splined to the shaft 55is a collar 57, which carries a pair'of oppositely disposed bevel gears 58 and 59. These gears are arranged to mesh with a bevel gear 60 fixed to a shaft 61 havingits axis parallel with that of armature 12, and journaled in the bracket 87 and also in bracket 39. Upon I this shaft-61 are fastened the pinions 62 and 63 which are in mesh with gears -14: and 1 5.

By sliding the collar 57 either to the right or left, eitherone or the other of bevel gears 58 and 59 may be made to mesh with the gear 60, and in this way cause rotation of the frame and brushes 15 and 16 in either direction. To'efi'ect this n'iovement of the collar, a lever 67 pivoted at 61 has a forked portion 65' engaging a groove 66 in the collar-57. The other end of this lever 67 is adapted to be pulled in one or the other direction by either of two eleetromagnets 68 and 69, in opposition to the force exerted by the two opposed springs and 71 acting on the lever 67 toreturn it to a neutral position, with neither of the bevel gears 58 or 59 in mesh with the gear 60. IVith neither I electromagnet '68 or 69 energized, these springs 70 and 71 maintain the lever 67 in its central position, and in this way rotation of shaft 55 is inetlcctive to rotate the brushes 15 and 16. In order to set. the'course by rotating these brushes, one or the other of the clectromagnets 68 .and69 is energized, as by a push button control, and during the energization one of the gears on collar 57 is in mesh with the gear 60 to effect the proper rotation of shaft 61 and brushes 15 and 16. In order to damp out any possible oscillations which might otherwise occur f0llowing an operation of either of the electromagnets 68 and 69, dash pots 72 and (u areprovided operatively connected with the end of lever 67. 1

An appropriate indicating device may be provided for showing the extent of rotation of the brushes effected by the arrangement just described. This indication may be transmitted to any desired point or points by the aid of well-known devices, such as by electromagnetic apparatus, although for the sake oi simplicity the indicator 74 is shown in thisinstance as 'mounted directly on the outside of frame29.' This indicator coacts with a dial 75, and is driven from the shaft 61 by the aid of a system of gears-such as the bevel gears 7 6 and 77'. Preferably I so choose the gear ratiosin this system that the indicator 74 moves over of shaft 61, since under such circumstances the actual meridian steered by may be 1Il(l1- rated by the pointer 74..

- with the frame 29 througha shaft 81 rotat ably mounted in the frame and carrying the pinions 82 and 83 which are in mesh with the gears 44 and 45. The shaft'81 may be i the same .angle as the brushes for a. definite amount of rotation.

appropriately supported by the aid of brackcts 37 and 39. When it is desired to set the brushes 15, 16 into a new position with respect to the body to be steered, the brake 78' may be released by the action of an electromagnet 84, arranged to be energized Whenever either of the two electromagnets 68 and 69 is energized.

If it be desired to maintain the axis of armature 12 more exactly in a vertical direction, use may be made of gyroscopes appropriately connected h) the axis of suspended frame 29 so as to augment the effect of the small amount of pendulo isness of the frame. A substantial amount of gyroscopic action is however produced by the rapid rotation of the armature 12. In this way the immunity of the system from short period ballistic. disturbances may be materially increased.- Furthermore since the operation of the entire instrument is based upon the induction of electromotive forces by the rotation of the armature 12 in a component of terrestrial magnetism, it is important to prevent the distortion of this magnetism to the greatest possible extent. For this purpose there should beno soft iron or other magnetic'niaterial in the vicini ty of the armature; and stray fields from electromagnetic apparatus such as motor 17 and electromagnets 68, 69 and 8d should be min mized by locating them at a distance, and if necessary by screening them by means of a light iron screen85. This screen serves to intercept the stray fields of the leakage fluxes.

In addition it is preferable to use alternatin current magnets instead of direct current.

\Vires carrying currents in the vicinity of the armature 12 should be so paired 01f 'or associated with each other as to'form substantially perfect bifilar systems with negligible external magnetic etl'ectsu When all these precautions are taken, the fieldof terrestrial magnetism is maintained uniform, and the disappearance of potential difference across the brushes l5 and 16 while the armature 12 is 1'0- tated, indicates that the brush axis, and

therefore the horizontal axis of reference of the stabllizedbody, is in a definite angular position with respect to the direction ofthc horizontal component of the terrestrial mag netism. 1

The instr'ument'of Figs. 2 and 3 if operated at a. speed high enough and if constructed to have a large enough number of turns in series with the brushes- 15 and 16, is capable of gen erating an E. M. F. which is more than suflicient to provide fects. v

Returning now to the. circuit diagram of Fig. 1, the brushes 15 and 16 are shown as connected'to the terminals of a very high resistance 86. The value .of this resistance is the necessary controlling efmade many times greater than the resistance r of the armature. 12, so that the difierence of potential of the terminals 87 and 88 is very nearly equal at all times to the E. M. F. induced in the armature.

In order to amplify the controlling effects, the thermionic tubes 26, 27 and 28 are utilized. The central point 89 of the resistance 86 is connected to the filament 90 of the first tube 26. This tube is shown as being provided with two controlling grids 91 and 92, and two plates 93 and 94, the grid 91 being disposed between filament 90 and plate 93, and grid 92 between filament 90 and plate 94. It is thus seen that this tube 26 is a double tube of the so called pliotron type, and has two input and two output circuits. The terminal 87 of resistance 86 is connected to grid 91, so as to affect the output current between filament 90 and plate 93. The terminal 88 is similarly connected to the grid 92, so as to affect the output current between filament 90 and plate 94. The heating of the filament 90 may be effected by the aid of the battery 95. A source of direct current E. M. F. such as the battery 96 is used for the plate or output circuits, which may be traced as follows: from the lower positive terminal 107 of battery 96, through wires 97 98, to point 99, where the current divides-one branch flowing through adjustable resistance 100, contact finger 101, the primary 102 of a transformer 103, plate 93, filament 90, point 104, wires 105 and 106, to the upper negative terminal 108 of battery 96. The other branch from point 99 flows through adjustable resistance 109,

contact finger 110, the primary 111 of a transformer 112, plate 94, to filament 90, from which the two currents flow in the same path to the'negative terminal 108, through wires 105 and 106.

As is now well known, the properties of such a vacuum tube as 26 are such that the plate currents flowing through the circuits just traced may be varied by varying the potentials of the controlling grids 91 and 92 relative to the filament 90. Thus if this potential is positive, the plate current is increased, and if itis negative, the plate current is reduced. The connection of the grids 91 and 92 to the terminals 87 and 88 of resistance 86 provides a means for varying these plate currents in response to the variations in the position of brushes 15, 16 relative to the direction 13 of the horizontal component of the terrestrial magnetism. Thus while the brushes are in the zero E. M. F. position, the potential difference between filament 90 and either of grids 91 and 92 is zero; Assuming that transformers 103 and 112 are similar, resistances 100 and 109 equal, the-plate currents in the two branches are equal. If however the brushes are displaced a slight amount in a clockwise direct-ion, which as we have already assumed, makes brush 15 positive with respect to brush 16, then grid 92 is positive with respect to the filament 90, while grid 91 is negative with respect thereto. This causes the plate current between filament 90 and plate 94 to be greater than that between this filament and plate 93. The potential drop across resistance 109 is therefore greater than that across resistance 100. Since one terminal of each of these resistances is connected to the positive terminal 107 of battery 96, this variation in drop causes the negative terminal 113 of resistance 109 to be at-a lower potential than the negative terminal 114 of resistance 100. This difference in potential between points 113 and 114 is much greater, due to the amplifying effect of the tube 26, than the potential difference across brushes 15, 16.

Had the brush axis been displaced in a counter-clockwise direction, the effects just noted would have been reversed, with the ultimate effect that point 113 would have been at a higher voltagethan the point 114. The potential difference between these two points is dependent solely upon the deviation of the brush axis from the zero E. M. F. position, and represents one of the elements upon which the control is based.

The transformers 103 and 112 having primary coils 102 and 111, and secondary coils 115 and 116, are provided for contributing another element to the control which is proportional to the velocity of the deviation, or in other words to the first derivative with respect to time of this deviation. WVhile the currents through the primaries 102 and 111 are steady and unva-rying, there can be no E. M. F.s induced in the secondary coi. 115 and 116. This condition is that when the brushes 15 and 16 occupy asteady position, or in other words, while there may be a deviation of the body there is neither an increasing nor a decreasing deviation. Thus the transformers are ineffective to create an E. M. F. when the deviation is steady. However, as soon as the brushes move, the currents through the primaries 102 and 111 vary, and the rate of variation is substantially proportional to that of the angular velocity of the brushes 15, 16, due to the fact that the variation in plate current through tube 26 may be made to be proportional to the variation in the grid potential. Such a variation in current induces an E. M. F in the secondaries 115 and 116. If both transformers 102 and 111 are wound in the same direction and coils 115 and 116 have their lower terminals connected, as shown, then it can be demonstrated by Lenzs law of induction that an increase in current in primary coil 111 due to a clockwise movement of the brushes, and a corresponding decrease in current in coil 102 causes E. M. F.s to be induced in the coils 115 and 116 in the direction shown by the arrows placed near the coils. Thus the upper terminal of coil 116 is positive, while that of coil 115 is negative, as regards the common lower terminal. Movement of the brushes in a counterclockwise direction afiects the-potentials of the coils 115 and 116 in the opposite sense, making the upper terminal of coil 115 positive as regards the terminalof coil 116.

In order to aii'ect the generator21 in response to these varying relative potentials, the generator is provided with pairs of opposed exciting coils 117, 118, and 119, 120. The coils 117 and 118 are connected in the plate circuits of the second tube 27. The filament 121 of this tube is heated by battery 95, and is connected, by the aid of yvire 106 to the negative terminal 108 of ba tery 96. The control grids 123 and 124 are connected respectively to terminals 114 and 113 of the resistances 100 and 109. Under the conditions we have assumed heretofore, the grid 123 will be positive with respect to grid 12 1, with the result that more current will be permitted to flow in the plate circuit controlled by grid 123 than in that controlled by grid 124. The plate circuit controlled by grid 123 includes battery 96, a switch 122, coil 117, plate 125 and filament 121. The plate circuit controlled by grid 124 includes battery 96, switch 122, coil 118, plate 126 and filament 121. The coil 117 normally exactly annuls the effect of soil 118, when the grids 123 and 124 are at the same potential, which condition corresponds to zero deviation of the brushes. A deviation in a clockwise direction as has been assumed, thus increases the current through coil.117 and decreases it through coil 118. The result is that the latter coil is overpowered, and an appreciable excitation is sup plied to the generator 21. This in turn causes the generation in this machine of an E. M. F. which is substantially proportional to the deviation of the brushes 15, 16. Since the motor 20 is connected directly to the generator 21,.-

therudder 170 or other stabilizing element is moved with a speed proportional to the brush deviation by-means of themotor shaft 25. The connection between the shaft and the rudder 170 must of course be such that the rudder will be moved tobring the body to be stabilized back to its desired position. In order -to insure substantial proportionality between the deviation of the brushes and the speed of motor 20, the tubes 26 and 27 are operated on that portion of the tubes characteristics which is linear, as is well understood. This linear characteristic is of great importance,and"it has been assumed'herein that double tubes of the sort illustrated can be constructed to provide this linear char acteristic, and that no material interference exists between the two electron paths in the tubes. This condition can of course be still more closely approximated with tubes having only single grids and anodes, as in some of the later modifications which I shall describe. For this reason also it isadvisable to work machines 20 and 21 below their saturation point. If the brushes were dlsplaced in a counter clockwise direction, then by tracing out the corresponding variations in current flow, it is possible to show that coil 118 receives more current than coil 117, with the result that the E. M'. F. generated in generator 2 1 is opposite in sense to What it was in the first case, and the motor 20 is rotated in a reverse direction, but in the proper direction to bring the body back to zero deviation. The excitation for the motor 20 is effected by means of coil 127 connected in series with an adjustable resistance 128 and fed froni any appropriate D. C. source such as the battery 96. I

lVhile the coils 117 and 118 are made to excite the generator 21 to an extent which is proportional to the brush deviation, the coils 119 and 120 produce an excitation which is proportional to the velocity of deviation. For this purpose'these'coils are located in the plate circuits of the thermionic tube 28. The battery 96 is again used for the source of potential in this circuit, and its negative terminal) '108 is connected to filament 129 of this tu e. common lower terminal of secondary coils 115 and 116. The control grids 130 and 13]. are respectively connected to the upper terminals of the coils 115 and 116; as is evident the potential of these grids are equal when the deviation is steady. Under such circumstances the plate currents are both equal; one through battery 96, switch 122, coil 1 19 and plate 132, the other through battery 96,

switch 122, coil 120 and plate 133, to filament 129 and thereby back to the negative terminal of battery 96. .Ifhowever, the deviation increases in a clockwise direction, grid 131-becomes positive with respect to grid 130, and

more current flows through coil 120 than through coil 119. The result is a proportional additional excitation for generator 21,

in the proper direction to influence the motor 20 to wipe out this velocity of deviation. For velocity in a counterclockwise direction, opposite effects are obtained, and coil 119 would overpower coil 120.

From the foregoing considerations, the operation of the device to produce dead beat steering may now be explained. As the deviation increases from zero say in a clockwise direction, coils 117 and 120 will predominate, and they will assist each other to wipe out both deviation and, velocity of deviation. The coil 120 thus produces a properly timed meeting action, which gradually reduces to zero as the speed of deviation vanishes. Under such circumstances the coil 117 alone controls the apparatus. When the body starts to swing back, the coil 117 still predominates over coil 118, but now coil 119 overcomes 120 and produces properly timed easing action, opposed to that of the the judgment of the helmsman, with the result that'the actions were not very accurately produced. On the other hand, the arrangement just described automatically produces these actions at the proper time, and there is an attendant very rapid wiping out of any deviations due to accidental disturbances.

, If the body swings in a reverse or counter clockwise direction, the meeting and easing actions will of course be also reversed, so that again the proper forces are brought into play to return the body to its undeviated that both of the exciting coils 41, 42 for the position and keep it there.

In the diagram of Fig. 1 I show the electi-oinagnets 68, 69, and 84, connected to the battery 96 or other source, which magnets as explained hereinhefore are utilized for setting the course of the body. Push buttons 134 and 135 may be utilized to energize the magnets. Thus while button 134 isoperated, magnets 69 and 84 are energized, and the brushes 15, 16 are moved in one direction by the aid of the transmission and gearing shown in Fig. 2. If however push button 185 be operated, then magnets 68 and 84 are energized andthe brushes are moved in the other direction. This system of brush shifting affords a very simple and convenient means for steering the vessel or airplane manually, if it be necessary to reset the course at any time. While the brushes are being set by this means, the body is turned to the new course by the aid of the controlling devices just described, wherein the inequality of the currents in branches 1.00, 102 and 109, 111, causes a prompt response by the rudder to turn the vessel to the new position corresponding'to the setting of the brushes.

I also show in Fig. 1 the coils 41, 42 which have an axis always perpendicular to the line of the brushes. These coils may be used optionally to increase still further the effect of any slight brush deviation. By opening the switch 122, it is possible to render these coils active, since then the short circuit across the terminals of'the coils is removed. When this is accomplished, current may enter through collector rings and 51, into coils 41, 42 respectively and returnthrough wire 136 and ring 49 to any appropriate source,

such as battery 96. Since the coils 41, 42

are Wound in opposite directions and have equal numbers of turns, they are ineffective to influence the E. M. F. across brushes 15, 16 when the current flow is the same in each. This is the condition when there isne'ither any yaw nor any velocity of yaw, as is apparent by tracing the complete circuit for these coils. The circuit for coil 41 may be traced from positive terminal of battery 96, collector ring 49, wire 136, coil 41, collector ring 50, exciting coils 117- and 120 in parallel, plate circuits 125, 121 and 133, 129 in parallel to the negative-terminal of battery 96. The

circuit for coil 42 is similar, except that it flows through coils 118 and 119 in parallel, as well as plate circuits 126, 121, and 132, 129. While there is no yaw, the current through plate circuit 125, 121 and coil 117 is equal to that through circuit 126, 121 and coil 118; and while there is no velocity of yaw the same may be said of the plate circuits in which coils 119 and 120 are located. Under such circumstances, therefore, the combined current through coils 117 and 120 is equal to that through coils 118 and 119, so

instrument 11 receive the same current, and their magneto-motive forces are entirely neutralized. If however, there is a slight amount of yaw say in a clockwise direction, more current flows through coil 117 than through coil 118, with the result that the current through exciting coil 41 is greater in proportion than through coil 42. For a clockwise velocity of yaw, this effect is still more pronounced, since more current flows through coil 120 than through 119. Thus during this stage of the angular motion, the magnetomotive force of coil 41 will overpower that of coil 42, and the resultant vector of transverse magnetization H will be directed to the West. This vector in combinationwith the horizontal compo nentof terrestrial magnetism H produces a resultant horizontal magnetizing force H greater in magnitude and forming a larger angle oz,- with the line of brushes than merely the component H of the terrestrial magnet-I ism. This results in the building up of an increased voltage across brushes 15, 16, and consequently still greater action H of the coils 41, 42 and so on. Upon reversal of the angular velocity of the ship, the action of the velocity control effected by'the relay 28 serves to reduce the angle a, with a consequent reduction in thecomponent H It is thus seen that the action of the cross magnetizing coils 41 and 42 serves to emphasize or magnify the actions of the relavs 27 and 28 which act in response to the positional function and to higher time derivatives there- 'of. It is importaht, when cross magnetizing coils such as 41, 42 are used, to be certain that conditions are not created under which the whole system becomes self excited. If that should happen the circuits would have such flow of currents as would bring the vacuum tubes to thecpoint of saturation, without the continuity of regulation as a function of the disturbing angular motion. It is important therefore in this case when such coils 41, 42 are ;used, not to increase either the amplificatioh of the vacuum tubes or the coeificient of mutual inductance between thecoils 41, 42 and th'e armature 12 beyond a certain critical value, at which the system becomes self-excited. In case the coils 41, 42are not used, it is of course possihlc to provide for any desired amplification, since under such circumstances self-excitation can never occur.

With the device as thus described, it is impossible for the vessel or other object to deviate to any substantial degree from her course. Even in the case of aerial navigation, where disturbing accelerations may act very persistently and disturb the direct ion of freely suspcnde d objects from the Vertical, my de vice as described prevents all possibility of extensive yawing, and the result is that the centrifugal horizontal accelerations are also reduced, if not entirely eliminated. It is thus possible to preserve the vertical position of armature 12 very accurately. Even if this were not possible, and if the armature should happen to precess in space so as to trace the cone 0, 1, 2, 3, 4, about the true vertical ()V of Fig. 7, the directional properties of the automatic steering derived from the position of the armature are not materially alfected. The only difference will be that only the values of the controlling forces will be altered slightly, but not their directions. Thus in Fig. 7 if OH represents the direction of the terrestrial magnetism, the armature 12 will be the more strongly excited the nearer its axis is to a position perpendicular to this direction. Thus if the. armature axis is in the position 01, the exciting component of OH is OH which is larger than if thcarmature were in the truly vertical position OV. In

this vertical position the exciting component of OH is represented by 0111,. If however the armature axis swings toO3, the exciting componept reduces to CH which is less than in either 6f the other cases, since the direction 03 is more nearly parallel with OH than these prior discussed positions. The only effect of this precession or deviation therefore is to weaken or strengthen the excitation of the armature 12, but the position about which the body is finally stabilized is not at all altered.

Inthe embodiment of my invention illustrated in Fig. 1, I show two separate tubes 27 and 28, one producing a positional controlling action, and the other a velocity controlling action, which actions are transmitted to the exciting coils 117, 118, 119, and 120.. Instead of combining the controlling actions in thefieldof generator 23, it is possible to combine them in other ways. In Fig. 4 by way of'a further example I have shown this combination eflected in the circuits for controlling a vacuum tube 137, which tube replaces the two tubes 27and 28 of Fig. 1. The grids 91 and 92 of the tube 26 in Fig. 4 are connected to resistance 86 in precisely the same manner as before. but 111 the plate circuits are inserted the variable inductances 138 and 139. The points 140 and 141 are connected to the grids 142- and 143 of tube 137. As long as the currents through the plate circuits 100 138, and 10)-13$), of. tube 26 are steady and unvarying, which corresponds to either zero deviation or to a constant deviation of the stabilized body from its position, the potential ditl'erences between points 99 and 140 on one hand, and points and 141 on the other hand are due solely to the ohmic drop across the resistances and It these currents are varying, however, additional elect-romotive forces appear. which are due to the self induction of coils 1218 and 139. These E. M. F.s are equal to where L, and L denote the coellicients of self induction of coils 138 and 139, and i, and i the instantaneous values of the currents in the branches 100, 138 and 109,139. The action of coils 138, 139 on the circuits of vacuum tube 137, and therefore on the controlling equipn'ient, is exactly the same as the action of transformers 103, 112 and tube 28 of Fig. 1. Only two exciting coils HA, 1 15 are needed, which are. dilfcrentially arranged and are located in the plate circuits of tube 137. The wires 141-6 may lead to collector rings 49, 50 and 51 as in Fig. 1 for the purpose of utiliz ing the coils 11, 42 on the armature 12, and thus of obtaining a sharper and quicker response of the apparatus. By varying the amount of resistance or inand du'ctance in series with the grid controlling circuits in the'embodiments shown in Figs.

1 and 1 as by means of the sliding contacts 101, 110, and 1 17, 148, it is possible to regulate the performance of the automatic steering device to meet widely varying conditions of navigation. Thus for example when the sea is quiet and it is' desired to steer a very accurate course, more resistance and inductance will he introduced in the circuit. and

the device will respond even to very slight deviations of the ship from her course, as well as to very small angular velocity of vawing.

Should however the sea be rough, when it is unnecessary and undesirable to have the vessel react against each individual impulse or wvave, and it is merely desired to maintain tions by means of contacts 101 and 110, the

steered course can be variedslightly or adjusted without 'making use of the brush shifting arrangement. Finally when under the influence of wind, trim and other factors,

the ship or other steered body has any tendency to yaw to one side moreviolently than to the other, this tendency to unsymmetrical yawing can be counteracted by oil'- settingthe controlling inductances in opposite directions by means of the sliding contacts 147 and 148, until the required counteracting effect is obtained.

In Figs. 1 and 4, controlling effects are obtained which are responsive only to t1 e extent of deviation and to the first derivative with respect to time of this deviation. It is a simple matter to extend the principles enunciated herein to provide controlling effects based upon higher time derivatives of the deviation. Thus in Fig. 1 if primary coils of transformers be inserted in the plate circuits of tube 28, between plates 132 and 133 and coils 119 and 120, and if the secondary E. M. Fis be impressed on the grids of an additional tube in the same manner as explained in connection with grids 130 and 131 of tube 28, I may obtain from such an additional tube a controlling action in phase with and proportional to the angular acceleration of the yaw. In an entirely, analogous manner still higher time derivatives may be obtained for the controlling actions, and thus as rapid and as sharp anticipatory actions as desired in the control either for stabilizing or steering may be produced. By giving predominance to the accelerational control, the controlling action will be started always in phase with the disturbing torque,

since this torque in virtue of the fundamental law of dynamics is in phase with the angular acceleration. In" this way the disturbing forces are made of no effect by neutralizing the disturbing torque, as distinguished from the older systems based only on positional control, wherein no counteraction is produced until the effect of the disturbing torque (that is, the deviation) has developed. The controlling actions excited by my sys-- tem will be practically devoid of any time lag since it is a well known fact that thermionic vacuum tubes have no inertia lag and react substantially. instantaneously to the grid control. Dueto this continuity of the control the rudder is moved by the motor 20 continuously in step with the control taking place on the field of the generator 23, fl. whole performance is rendered rapid and continuous.

Instead of using the called Ward Leon- I ard system of control shown in Fig.1,which is based upon the use of a variably excited generator 23; feeding a constantly excited motor 20, it is obviously possible to use other control systems such as relays, solenoids, electromagnets and the like to accomplish substantially identical controlling functions.

In the embodiments thus far described, the controlling effects are immediately utilized to bring back the body to a certain predeten;

nd the.

5,'where the small motor 149 is actuated to rotate the gear 150 driving the brushes around the shaft 18 of armature 12. Of course in this case the controlling system need not be so refined as in the case where the steered body is controlled. The follow up motor 149 may readily be controlled from thesystem shown in Fig. 4. There are two oppositely Wound field coils 151 and 152 in series with the armature of motor 149. These coils are in the plate circuits of a tube entirely similar to tube 137 of Fig. 4, the lead 153 going to the left hand plate, lead 154 to the right hand plate, and lead 155 to the positive terminal of battery'96. The effect of the control in response to velocity of deviation is to eliminate hunting of the follow up motor 149, which is generally highly undesirable. This motor as shown in Fig. 5 is capable of performing other functions in addition to or in place of its follow up duty,

such as for controlling functions used in connection with gyroscopic compasses, as for example to actuate remote control indicating repeaters, to impress controlling movements upon automatic steering devices of vessels, and the like. It would of course be also possible to provide here also, coils such as 41, 42

of Fig. 1 if greater sharpness of the follow up performance is desired. When so used these coils can be operated either below or above the point of self-excitation; in general,

it is more desirable to provide such coils in the case of a follow up system such as shown in'Fig. 5, and even to adjust them above the point of self-excitation than in the s stem of I 1 or 4. In this instance the plates 93 and 94 I r are located one in each tube, and there are also two filaments 90 and '90. The grids 91 and 92 connect, by the aid of leads 158 and 159, with opposite terminals of a resistance such as 86 of Fig. 1. The leads'160 and 161 from the plates 93 and 94 connect to appropriate resistances and inductances as illustrated in the prior figures. In all respects the control when using such single tubes may be made identical with those already de scribed. -In other respects also, various modifications may be resorted to in the schemes shown. Thus still other types of vacuum tubes may be utilized, or in tact other sensitive relays such as of the polarized type may be substituted to perform the follow up functions although without the continuity of action atl'orded by vacuum tubes.

I claim:

1. In a system l'or stabilizing a body about a definite direction, a dynamo electric machine adapted to be excited by the field of terrestrial magnetism to a substantial degree, and means for controlling the body by the aid of the elcctromotive torce generated by said machine, comprising means atl'ecting the body in such manner that its controlling action on the body varies with each variation of the said electromotive force.

2. In a system for stabilizing a body about a definite. direction, a dynamo electric armature rotating in the field of terrestrial magnetism, a pair of brushes tor the armature, stationary relatively to the body. and means for continuously controlling the position of the body so as to maintain the E. M. F. across the brushes at a minimum, comprising means affecting the body in such manner that its controlling action on the body 'aries with each variation of the said electromotive force.

3. In a systemtor stabilizing a body about a definite direction, a dynamo electric machine adapted to be excited to a substantial degree by the field of terrestrial magnetism, the position of the axis of the machine having a definite direction with respect to the body.and means for continuously controlling the position of the body in accordance with the EQM. F. generated in the machine and varying with each variation of the position of the body with respect to the terrestrial field.

4. In a system for stabilizing a body about a definite direction, means for generating an E. M. F. substantially proportional to the deviation of the body from a predetermined magnetic meridian, and means for continuously controlling the body in accordance with a function of this E. M. F., comprising means affecting the body in such manner that its controlling action on the body varies with each variation of the said electromotive force.

5. In a system for stabilizing a body, means for creating an eleetromotive toree that is substantially continuously variable in aecordzmm with the extent of deviation of the body from the desired position, and means for controlling the body to return it to its desired position, in accordance with a function of the electromotive force, comprising means atlecting the body in such manner that its controlling action on the body varies with each variation of the said elcctromotiveforce.

6. In a system for stabilizing a body about a definite direction, a dynamo electric armature adapted to generate an E. M. F. by rotation in the terrestrial magnetism, a pair of brushes for tapping the armature having a definite axis with'respect to the body to be stabilized, and means for continuously controlling the position of the body in accord ance with a function ot the E. M. F. across the pair ot brushes. comprising means altecting the body in such manner thatits controlling action on the. body varies with each vari ation of the said electromotive force.

7. In a system for stabilizing a body about a definite direction, a dynamo electric armature adapted to generate an E. M. F. by rotation in the terrestrial magnetism, means for n'iaintaining the axis of the armature vertical, a pair of brushes stationary relative to the body for tapping the armature, and means for continuously controlling the position of the body'in accordance with a function of the E. M. F. across the brushes, comprising means altecting the body in such manner that its controlling action on the bodyvaries with each variation of the said eleetromotive force.

ti. In a system for stabilizing a body about a definite direction, a dynamo electric armature adapted to generate an E. M. F. by rotation in the terrestrial magnetism, a pair of brushes tapping the armature at points stationary relative to the body, and means for controlling the body in accordance with the value'of the E.- M. F. across the brushes" and also with the value of the rate of change of the E. bl. F.

9. In a' system for stabilizing a body about a definite direction, a dynamo electric armature adapted to generate an E. M. F. by rota.- tion in the terrestrial magnetism, means for tapping the armature at points stationary with respect to the body, a member for controlling the position of the body, and means for moving this member with a speed corresponding to a function of the E. M. F. across the tapped points, said speed varying with each variation of the said electromotive force.

10. In a system for stabilizing a body about a definite direction, a dynamo electric armature adapted to generate an E. M. F. by rotation in the terrestrial magnetism, means for tapping the armature at points stationary with respect to the body, a member for controlling the position of the body, and means for moving this member with a speed corresponding to the E. N. F. across the tapped points and the rate of change ot this E. M. F.

ll. In a system for stabilizing a body about a definite direction, means for producing an E F. which varies substantially in proportion to the extent of deviation of the body. means for deriving an E. M. F. from this first E. M. F. which varies substantially ltll) ill?) body.

in proportion to the rate of change of the first E. M. F., and means for controlling the position of the body in accordance with a function of the values of these E. M. F.s.

12. In a system for stabilizing a body about a definite direction, means for producing an E. M. F. which varies substantially in proportion to the extent of deviation of the body, means for deriving an E. M. F. from this first E. M. F. which varies substantially in proportion to the rate of change .of the first produced E. M. F a rudder-like member for controlling the position of the body, and means for moving this member with a speed corresponding to a function of the values of the E. M. F.s.

13. In a control'system, means for generating an E. M. F means for deriving an E. M. F. which varies substantially in proportion to the rate of change of the generated E. M. F. and a controlling means affected by both of these F.s.

14. In a system for stabilizing a body about a definite direction, means for generating-an E. M. F. which varies substantially in proportion to the deviation of the body from its required position, means for deriving an E. M. F. which varies substantially in proportion to the rate of change of the generated E. M. F., and means, affected by both these E. M. F.s, for controlling the position of the 15. In a system for stabilizing a body about a definite direction, a dynamo electric armature rotated in the terrestrial magnetic field, a pair of brushes for-tapping the armature at points that are relatively stationary with respect to the body, means for further exciting the machine along an axis having a constant relation with the axis of the brushes, said means becoming energized upon movement of the body from its desired position, and rudder-like means for controlling the position of the'body, affected in accordance with the E. M. F. across the brushes.

16. In a system for stabilizing a body about a definite direction, a dynamo electric arma ture rotated about an axis having a definite relation to the body to be stabilized, means for exciting the armature in a direction corresponding to the direction of the terrestrial magnetic field, a pair of brushes tapping the armature on an axis that is stationary with respect to the body to be stabilized, means for energizing the armature about an axis fixed with respect to that "of the brushes, anda rudder like member for controlling the position of the body, afiected in accordance with the E. across the brushes.

17. In a system for stabilizing a body about a definite direction, a dynamo electric armature rotated in the terrestrial magnetic field so as to be influenced thereby, means for maintaining the axis of the armature substantrolling the position of the body, and means for moving this member at a speed corresponding to a function of the E. M. F. generated across two points of the armature which are stationary with respect to the body to be stabilized.

18. In a system for stabilizing a body about a definite direction, a dynamo electric armature rotated in the terrestrial magnetic field so as to be influenced thereby, means for maintaining the axis of the armature substantially vertical, arudder-like member for controlling the position of the body, a motor for moving said member, and means for impressing upon the motor an E. M. F. which is a function of the E. M. F. generated in the dynamo electric machine across tWo points which are stationary with respect to the body to be stabilized, said impressed E. F. M. varying with each variation of the generated '19. In a system for stabilizing a body about a definite direction, means for producing an E. M. F. varying substantially in proportion to the extent of deviation of the body, means for amplifying said E. M. F., a rudder-like member for controlling the position of the body, and means for moving this member with a speed corres onding to a function of the amplified E. F., said speed varying pith each variation of the said electromotive orce.

20. In a system for stabilizing a body about a definite direction, a dynamo electric armature rotating about a vertical axis, means for exciting the armature in accordance with the horizontal component of the terrestrial magnetism, means for tapping said armature at a pair of points that are stationary relatively a definite direction, means for generating an E. M. varying substantially in proportion to the deviation of the body'from its required position, an electronic emission device. for amplifying the variations in this E. M. F. both as to direction and amount, and means for controlling the positidn of the body, operated in response to a function of the E. M. F.

. 22. In a system for stabilizing a body about a definite direction, means for generating an E. M. F. varying substantially in proportion to the deviation of the body from its required position, an electronic emission device for am lifying the variations in this E. M. botii as to direction and amount, a rudder-like member for controlling the position of the body, and means for'moving the rudder-like member at a speed substantially pro portional to a function of the E. M. F. generated.

23. In a system for stabilizing a body about a definite direction, a dynamo electric machine excited by the horizontal component of the terrestrial. magnetic field, means for tapping the armature at a pair of points stationary relative to the body to be steered, an electronic emission device for amplifying the variations in the E. M. F. a cross the points, both as to direction and amount, and means for controlling the position of the body operated in accordance with the amplified variations and also with a time derivative of the variations.

24. In a system for stabilizing a body about a definite direction. means for generating an E. M. F. varying substantially in proportion to the deviations of the body from its required position, both in direction and amount, an electronic-emission device for amplifying this E. M. E, a generator, means for exciting this gcneratorin accordance with the amplified E. M. F. and also in accordance with a time derivative of the/E. M: E. a motor fed from the generator, and. a rudder-like men1- ber moved by the motor.

25. In a system for stabilizing a body about a definite direction, a rotating dynamo electric armature for generating an E. M. F. occasioned by the field of terrestrial magnetism, a pair of brushes tapping the armature at points stationary relative to the body to be stabilized, a resistance having a high value compared with that of the armature. said brushes being connected across the resistance, an electronic emission device having a pair of control electrodes also connected across the resistance, and an electron emitting electrode connected to a central point of the resistance, a pair'of output circuits for the device, each including a resistance, a generator, means for exciting the generator in accordance with the difference in the potential drop 7 across the two resistances in the output circuits, a motor fed from the generator, and a rudder-like member-moved by the motor. 26. In a system for stabilizing a body about a definite direction, the elements as set forth in claim 25. with the addition of an inductance in each of the output circuits, and additional means for exciting the generator in accordance with this difference in potential drop across the two inductances.

27. In a system for stabilizing a body about a definite direction, the elements as set. forth inclaim 25, with the addition of an inductance in each of the output circuits, additional means for exciting the generator in accordance with the difference in potential drop across the two inductances, and a pair of electronic emission'devices for amplifying the effects of these differences in potential drops.

28. In a directional responsive electric system, a dynamoelectric armature excited by the field of terrestrial magnetism, a pair of brushes stationary relatively to the body, means for controllingthe position of the body operated in accordance with variations in E. M. F. across the brushes due to variations in position of the body, and means for accentuating the variations in E. M. F. comprising a coil for exciting the armature along an axis having a position constant with respect to that of the brushes, and means for energizing this coil in accordance with a. function of the E. M. F. across the brushes.

29. In a directional responsive electric system, the elements as set forth in claim 28 ,with the limitation that the accentuating coils are energized in accordance with the E. M. F. across the brushes and also with a time derivative of this E. M. F.

30. In a directional responsive electric system, the elements as set forth in claim 28, with additional means for energizing the generator substantially in accordance with a time derivative of the deviation.

31. In a system for stabilizing a body, means for creatingan electromotive force that is substantially continuously variable in accordance with the extent of deviation of the body from its desired position, means for creating another substantially continuously variable electromotive force that'is a derivative with respect to time of the first mentioned electromotive force, and means for controlling the body to return it to its desired position, in accordance with the combination of the two electromotive forces.

32. In a system for stabilizing a body, means for creating an electromotive force that is substantially continuously variable in accordance with the extent of deviation of the body from its desired direction, and means for producing a torque continuously dependent upon the value of this electromotive force for returning the body to its desired direction, said torque varying with each variation of said electromotive force.

33. In a directional responsive electric system, means for creating a substantially con tinuously variable electromotive force, that is a function of the directional condition of the device to be controlled, means for deriving from said electromotive force, another electromotive force varying as the ate of change of the first electromotive force, and means for creating a controlling effect in accordance with both of these electromotive forces.

34. In a directional responsive electric system, means for creating a substantially continuously variable electromotive force, that is a function of the directional condition of the device to-be controlled, means for deriv ing from said electromotive force, another electromotlve force that is a time derivative of the first electromotive force, and means for of the tapped points and the excitation, controlling means operated continuously in response to a deviation of the taps from a definite relative position with respect to the excitation, and means foraccentuating the potential diflerence variation between the tap points in response to such deviation.

36'. In a directional responsive electrical system, the elements as set forth in claim 35,

.vvith the limitation that the accentuating means comprise exciting coils having an axis fixed as regards the tap points and energized 20 in response to the deviation of the position of the tap points.

In testimony whereof, I have hereunto set my hand.

NICOLAI MINORSKY. 

